I have never had any success resetting an SEB Modem, it depends upon the firmware of the SEB. Only an authorised SEB Vendor has the necessary files to reset the SEB, for $300 they will reset if for you. The easiest thing to do if you need modem access is to replace the SEB with a USR Modem about $99. If yo do then you will need to initialize the modem to work with the PBX.
Get a standard AT Cable for you PC, set your communications software to either 2400 or 9600
Here is how:
Power off the modem
Set DIP Switches 1,3,7, and 8 down for all programming
Turn on Modem
at&f0 cr ok
ats0=1 cr ok
at&b1 cr ok
aty0 cr ok
atq1 cr no response
at&w0 cr no response
at&w1 cr no response
Power off the modem
Set DIP Switch 1, 4, and 8 down, all others should be up